1. Field of the Invention.
The present invention relates to a method for producing fine nickel powder that can be utilized as seed crystals from a solution containing a nickel ammine sulfate complex, and particularly, the present invention can be applied to the treatment of an in-process intermediate solution generated from a nickel hydrometallurgical process.
2. Description of the Related Art.
Examples of known methods for producing fine nickel powder include dry methods such as an atomizing method of dispersing molten nickel in a gas or in water to obtain fine powder and a CVD method of volatilizing nickel and reducing it in a vapor phase to thereby obtain nickel powder as shown in Japanese Patent Laid-Open No. 2005-505695.
Further, examples of methods for producing nickel powder by a wet process include a method of producing nickel powder using a reducing agent as shown in Japanese Patent Laid-Open No. 2010-242143 and a spray pyrolysis method in which nickel powder is obtained by pyrolysis reaction by spraying a nickel solution into a reducing atmosphere at high temperatures as shown in Japanese Patent No. 4286220.
However, these methods are not economical because they require expensive reagents and a large amount of energy.
On the other hand, a method of obtaining nickel powder by feeding hydrogen gas into a nickel ammine sulfate complex solution to reduce nickel ions in the complex solution as shown in “The Manufacture and properties of Metal powder produced by the gaseous reduction of aqueous solutions”, Powder metallurgy, No. 1/2 (1958), pp 40-52. is industrially inexpensive and useful. However, nickel powder particles obtained by this method are easily coarsened, and it has been difficult to produce fine powder that can be used as seed crystals.
Particularly, when particles are intended to be generated from an aqueous solution and grown, there is used a method of obtaining a powder having a predetermined particle size by allowing a small amount of fine crystals called seed crystals to coexist and feeding a reducing agent thereto to grow the seed crystals. Although seed crystals used in this method are obtained by grinding products in many cases, time and effort are required and the yield decreases, which leads to an increase in cost. Further, seed crystals having the best particle size and properties are not necessarily obtained by grinding. Thus, a method for stably obtaining seed crystals has been required.
In such a situation, the present invention provides a method for producing fine nickel powder used as suitable seed crystals for producing nickel powder from a solution containing a nickel ammine sulfate complex.